Monitoring systems for patients in a medical environment have long been known. These monitors include electrodes which are designed to be attached to the patient. The electrodes receive electrical signals which represent physiological functions in the patient. Some form of indication of the values of those signals is then displayed. For example, an electrocardiogram (ECG) system includes electrodes designed to be attached to the patient on the chest, inter alia. These electrodes receive electrical signals indicative of the instantaneous operation of the patient's heart. Images representing waveforms related to the ECG electrode signals are displayed on a display device for a doctor to analyze.
Recently, it has been recognized that, in a hospital setting, there are advantages to maintaining all monitoring data gathered from patients, and other data gathered about those patients, such as lab results etc., in a central location. Such an arrangement would allow patient information to be available anywhere in the hospital. Such an arrangement would also permit patient information, possibly derived from monitoring equipment, to be received and stored in the central location from anywhere in the hospital.
In the past, monitoring equipment was maintained at one fixed location, e.g. an examining room. Patients requiring that type of monitoring were moved to the room containing the monitoring equipment, and connected to the monitoring equipment. The monitoring equipment was plugged into the AC power socket at the fixed location. In addition, a direct wired connection between the monitoring equipment at this fixed location and the central storage location was maintained, making it easy to transfer monitoring data to the central location to be stored. However, recently, it has been recognized that in some cases it is important to maintain monitoring of a patient at all times; even those times when the patient is in transit, e.g. among patient room, examining room, operating room, etc. This requires that monitoring equipment be portable. By this method, the monitoring equipment may be transported along with the patient from one location to another. There are two aspects to enabling portability of monitoring equipment: first is supplying power to the monitoring equipment; second is maintaining a data link between the monitoring equipment and the central location, while it is in transit with the patient.
The aspect relating to providing power to the monitoring equipment was solved by including batteries in the monitoring equipment. One skilled in the art will understand that batteries require charging, and that patients are in transit a small fraction of the time. Current portable monitoring equipment includes fixed docking stations in all appropriate fixed locations, such as operating rooms, examining rooms and patient rooms. When a patient is in one of these locations, the portable monitoring equipment is inserted into the docking station at that location. These docking stations are connected to the AC power at that location, and provide charging current for the batteries in the monitoring equipment. This permits the batteries to maintain their charge. When a patient is moved, the monitoring equipment, with a charged battery, is removed from the docking station, and transported with the patient until another docking station is available.
Because the docking station is connected to AC power, and because it is well known that it is dangerous for electrical power to be applied directly to a patient, especially above the waist, standards-have been developed to ensure that all electrical power is isolated from electrodes intended to be attached to the patient. This has required that battery charging current be provided to the portable monitoring equipment without a direct electrical connection between the AC power socket and the portable monitoring equipment. This has been done using the known technique of split transformers in the form of a bobbin in the monitoring equipment which surrounds a magnetic core in the docking station when the equipment is docked. The AC current induces an alternating magnetic flux around the magnetic core in the docking station, which, in turn, induces a current in the bobbin in the monitoring equipment when docked. This current, in turn, provides operating power for the monitoring equipment and also maintains the batteries charged, all in a known manner. Operating efficiencies of around 60% may be obtained using this known system.
The aspect relating to maintaining a data link when the monitoring equipment is docked was solved by providing a wireless, e.g. radio frequency (RF), link for transmitting monitoring data from the monitoring equipment to the central location. Each piece of monitoring equipment includes an RF transceiver and antenna. Each docking station also includes a corresponding RF transceiver and antenna. In addition, free-standing antennae and transceivers are located throughout the hospital, in particular at locations where patients would be transported, e.g. halls, etc. Each of the transceivers in the docking stations and the free standing locations is connected by a wired connection to the central location. Using RF communications between the docking station and the monitoring equipment further provides electrical isolation.
When a patient is in a fixed location, and the monitoring equipment is placed in a docking station, the docking station receives the RF signal from the monitoring equipment and transmits the data to the central location via its wired connection. When a patient is in transit from one fixed location to another, the free standing antennae/transceiver locations receive the RF signal from the monitoring equipment and transmit the data to the central location. This provides the ability to monitor a patient continuously.
However, there are locations in which continuous RF transmissions from the monitoring equipment may cause problems and must be carefully planned for. For example, in operating rooms, electro-cautery machines use RF energy to cut tissue and coagulate blood during surgery. This instrument causes an unpredictable amount of RF energy and could possibly interfere with the RF link of the monitoring equipment. However, it is in this environment that it is most important that no monitoring data be lost or corrupted.
Monitoring equipment which is portable, in which power efficiency is higher than 50%, and in which potential RF interference is minimized is desirable.